Client-side Rendering vs Server-side Rendering

What's the difference between CSR and SSR and which one we should use.


Since the first Websites started appearing on the Internet, the most used method to build them has been Server-side Rendering (SSR). However, during the last decade, a new approach grew popular - Client-side Rendering (CSR).

Let's get into these techniques and their differences.

Server-side Rendering

SSR works by taking requests from the end-user, generating an HTML page on the server, and sending it to the browser. In other words, the server gets a new request each time you reload or request a new page. It doesn't matter if the new page has the same layout, or it's similar to the previous one.

This unequivocally leads to a lot of traffic to handle.

The most commonly used Server-side Language is probably PHP, despite NodeJS, C#, and other languages are slowly taking the lead.

Because the HTML file is already populated, SEO is easily implementable on each page. Web crawlers can see the page content right away.

Pros of SSR

  • Best option for SEO.
  • The initial load is a lot faster.
  • Doesn't require JavaScript to run correctly.
  • Can effortlessly communicate with databases (on CSR the source-code is public, we'd need an API in the middle).
  • Most suitable for static websites.

Cons of SSR

  • Time To First Byte (TTFB) is higher - bigger files.
  • More traffic, you'd need a server upgrade for handling more users.
  • Higher cost.
  • Less website interactivity (static pages).
  • Page reloads for every new page requested.
  • Problematic for slower Internet connections.

Client-side Rendering

Differently, CSR relies mostly on JavaScript. When the end-user lands on a client-side rendered website, the server sends to the browser an empty HTML file linked to a specific JavaScript file.

Instead of rendering the page on the server, JavaScript computes the page on the browser.

The loading time will be longer, but the downloaded file is smaller.

As CSR works directly on the browser, you can design engaging and accessible ways to interact with the user.

Above all, the most known CSR libraries at the moment are Angular, React, and Vue.

In CSR, the page sent by the server is like a template, it gets populated dynamically by JavaScript: this is what we refer to as dynamic web pages.

Pros of CSR

  • Time To First Byte (TTFB) is lower - smaller files.
  • Easier to implement. It uses client-side technologies, no need to manage the server.
  • There're lots of powerful JavaScript libraries.
  • More user interactions.

Cons of CSR

  • Worst option for SEO optimization: the page appears blank to any search engine.
  • JavaScript needs to be allowed on the browser.
  • Can't communicate directly with a Database, secrets would be publicly available.
  • The initial load can be heavier - lots of JavaScript code to run.